For freeze-drying, tuber pieces were placed in a freezer
(−20 ◦C) for three days. Afterwards, the frozen pieces were put
into a freeze-dryer (T = −76 ◦C, p = 1 bar, Christ Alpha 2-4 LSC
Freeze Dryer) for four days. The freeze-dried samples were
ground, and stored in a freezer at −20 ◦C.